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Synchronicity rules Synchronised movement such as military parades makes men feel more powerful and intimidates opponents, a new study suggests.

The findings are published today in the Royal Society journal Biology Letters.

Social animals such as humans have had to evolve ways of quickly deciding whether to fight or run when confronted by an opponent, says anthropologist, Professor Daniel Fessler, of the University of California, Los Angeles.

Fighting when you have a good chance of winning, running when you have a good chance of losing, and negotiating when that's the most successful approach is likely to improve your chance of survival.

While two lizards might just decide on the basis of individual size, other more complex animals use a range of factors to form a "mind's-eye image" of the threat posed by their opponent, says Fessler and colleague Colin Holbrook.

"You can think of it as a little picture in the mind. It's like a mathematical summary of variables that matter," says Fessler. "If the mind's-eye image is small you can attack, if it's big then you should run away."

According to Fessler, synchrony helps inform this picture.

For example, he says, some monkeys jump up and down in sync to intimidate their opponents.

"What synchrony is doing as a signal is saying we are able and motivated to act in concert and therefore we are a formidable fighting force," says Fessler.

Role of synchrony

To investigate the role of synchrony in forming the 'mind's-eye image' of the threat posed by an opponent, Fessler and Holbrook got 96 undergraduate men to walk in a pair, either in sync or at their own pace with their partner.

They then gave the participants a range of random questions to disguise what the experiment was about -- such as estimating the age of a woman in a photograph or how many colours of jellybeans there were a jar.

In between these "disguise tasks" the researchers showed participants a picture of an angry man and asked them to estimate how big and strong he was.

The participants used images showing men of different heights and musculature to build a composite of the angry man's body.

While the whole exercise was never framed as being about conflict, the results supported the idea that synchrony is a way of communicating the ability to win a fight, says Fessler.

"The participants in the synchrony condition thought that the man was smaller and less muscular than the participants in the 'walk at your natural pace' condition," he says.

Fessler say the study, which was funded by the US Air Force Office of Scientific Research, is the first experiment to show synchronised behaviour affects people's assessments in a conflict situation.

He says the findings could explain why military parades are still common at a time when armed forces increasingly rely on airstrikes.

Such synchronous exercises communicate strength both to other members of the group and to opponents.

While the experiment only involved men, he says previous work has demonstrated that the 'mind's-eye image' is used by both men and women to represent the threat that an opponent poses.

Synchrony and co-operation is not always associated with conflict, but Fessler says the good feeling it can give us to be part of a group in dance and religious rituals, for example, has its roots in deep history of inter-group conflict.

"In the past being part of a synchronised group meant my prospects were better," he says.